Inter-cell interference mitigation

ABSTRACT

A method and Coordinated Multi-Point (CoMP) cell controller for reducing interference in a wireless communication network in which a first CoMP cell neighbors a second CoMP cell. The CoMP cell controller in the first CoMP cell gathers scheduling information from border sub-cells in the neighboring second CoMP cell in which transmissions to and from UEs cause inter-CoMP cell interference in at least one sub-cell in the first CoMP cell. The CoMP cell controller augments intra-CoMP cell scheduling information in the first CoMP cell with the scheduling information from the border sub-cells to create augmented scheduling information. The CoMP cell controller then utilizes the augmented scheduling information to schedule transmissions to and from UEs within the at least one sub-cell in the first CoMP cell to reduce the inter-CoMP cell interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/167,925 filed Apr. 9, 2009.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX

Not Applicable

BACKGROUND

The present invention relates to wireless cellular telecommunication systems. More particularly, and not by way of limitation, the invention is directed to a system and method for mitigating inter-cell interference in Coordinated Multi-Point cells.

Inter-cell interference in a wireless cellular telecommunication network is one of the most dominant sources for performance impairment. Traditional approaches to mitigating this impairment include measures such as frequency reuse and spread spectrum. More recently, Inter-Cell Interference Coordination (ICIC) solutions that rely on the ad hoc coordination of multiple cells have also been proposed. See, for example, the Ericsson Contribution, “On Inter-cell Interference Coordination Schemes without/with Traffic Load Indication,” 3GPP TSG-RAN WG1 R1-072456.

SUMMARY

The present invention provides a system and method for reducing inter-cell interference within a CoMP architecture, which overcomes the shortcomings of the prior art.

In one embodiment, the present invention is directed to a method of reducing interference in a wireless communication network comprising a first CoMP cell and a neighboring second CoMP cell, wherein each CoMP cell comprises a plurality of contiguous sub-cells and a CoMP cell controller operative to manage transmissions within the sub-cells of the CoMP cell to minimize intra-CoMP cell interference. The first CoMP cell controller gathers scheduling information for an external sub-cell in the neighboring second CoMP cell, wherein the external sub-cell is located such that transmissions to and from user equipments (UEs) within the external sub-cell cause inter-CoMP cell interference in a given sub-cell in the first CoMP cell. Intra-CoMP cell scheduling information in the first CoMP cell is augmented with the scheduling information for the external sub-cell to create augmented scheduling information, and the first CoMP cell controller utilizes the augmented scheduling information to schedule transmissions to and from UEs within the given sub-cell in the first CoMP cell to reduce the inter-CoMP cell interference.

In another embodiment, the present invention is directed to a method of reducing interference in a wireless communication network comprising first, second, and third neighboring CoMP cells. The method includes the steps of defining a hierarchical scheduling order in which the first CoMP cell controller schedules transmissions in the sub-cells of the first CoMP cell, and then the second CoMP cell controller schedules transmissions in the sub-cells of the second CoMP cell, and then the third CoMP cell controller schedules transmissions in the sub-cells of the third CoMP cell; and after the transmissions in the sub-cells of the first CoMP cell are scheduled, gathering by the second CoMP cell controller, scheduling information for sub-cells in the first CoMP cell that border the second CoMP cell. The method also includes augmenting intra-CoMP cell scheduling information in the second CoMP cell with the scheduling information from the bordering sub-cells in the first CoMP cell to create augmented scheduling information for the second CoMP cell; and utilizing the augmented scheduling information for the second CoMP cell to schedule, by the second CoMP cell controller, transmissions to and from UEs within the sub-cells of the second CoMP cell to reduce the inter-CoMP cell interference with the first CoMP cell. After the transmissions in the sub-cells of the second CoMP cell are scheduled, the third CoMP cell controller gathers scheduling information for sub-cells in the first and second CoMP cells that border the third CoMP cell. Intra-CoMP cell scheduling information in the third CoMP cell is augmented with the scheduling information from the bordering sub-cells in the first and second CoMP cells to create augmented scheduling information for the third CoMP cell; and the third CoMP cell controller utilizes the augmented scheduling information for the third CoMP cell to schedule transmissions to and from UEs within the sub-cells of the third CoMP cell to reduce the inter-CoMP cell interference with the first and second CoMP cells.

In another embodiment, the present invention is directed to a CoMP cell controller in a first CoMP cell for reducing interference in a wireless communication network in which the first CoMP cell neighbors a second CoMP cell. The CoMP cell controller includes means for gathering scheduling information from a plurality of external sub-cells in the neighboring second CoMP cell, wherein the external sub-cells are located such that transmissions to and from UEs within the external sub-cells cause inter-CoMP cell interference in at least one sub-cell in the first CoMP cell. The CoMP cell controller also includes means for augmenting intra-CoMP cell scheduling information in the first CoMP cell with the scheduling information from the plurality of external sub-cells to create augmented scheduling information; and means for utilizing the augmented scheduling information to schedule transmissions to and from UEs within the at least one sub-cell in the first CoMP cell to reduce the inter-CoMP cell interference.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

In the following section, the invention will be described with reference to exemplary embodiments illustrated in the figures, in which:

FIG. 1 is an illustrative drawing of a simple example of a Coordinated Multi-Point (CoMP) cell with a schedule of users;

FIG. 2 is an illustrative drawing of three adjacent CoMP cells;

FIG. 3 is an illustrative drawing of a grouping of CoMP cells in a system deployment in an embodiment of the present invention;

FIGS. 4A and 4B are illustrative drawings of a scheduling hierarchy among a grouping of CoMP cells in an exemplary embodiment of the present invention;

FIG. 5 is a flow chart illustrating the steps of an embodiment of the method of the present invention;

FIG. 6 is a simplified block diagram of an exemplary embodiment of a CoMP cell controller according to the teachings of the present invention; and

FIG. 7 is a graphical representation of the uplink performance of the present invention compared to a conventional method.

DETAILED DESCRIPTION

One solution to mitigate inter-cell interference is to connect multiple cells to a central controller unit, which coordinates the transmission and reception to and from the User Equipments (UEs) so that interference can be avoided by scheduling, or can be actively suppressed using signal processing techniques. This type of solution may be referred to as Coordinated Multi-Point (CoMP) transmission and reception. In this context, a “CoMP cell” is a collection of geographically contiguous cells, referred to as sub-cells, connected to the same central control unit.

FIG. 1 illustrates a simple example of a CoMP cell 10 comprising seven sub-cells numbered 0 through 6, a CoMP cell controller 11, and a “schedule” 12 generated by the CoMP cell controller. The schedule is essentially a list of users being served at different times. The triangles represent the UEs in different cells scheduled in a first time interval, the squares represent the UEs scheduled in a second time interval, and the circles represent the UEs scheduled in a third time interval. There is no particular relationship among UEs designated by the same shape in this example; they just happen to be scheduled to be served at the same time.

The information to be communicated to the CoMP cell controller may be as simple as the path gains between the UEs and the base stations. However, the optimal schedule list under certain constraints may be difficult to determine since the typical number of users in the system makes the hypothesis space prohibitively large for an exhaustive search.

FIG. 2 is an illustrative drawing of three adjacent CoMP cells (A, B, and C), each comprising a number of sub-cells. In a CoMP architecture, the interference between sub-cells is only coordinated or suppressed within each CoMP cell. In the context of CoMP, this type of interference between sub-cells in a single CoMP cell is referred to as intra-CoMP-cell interference. However, there is no coordination between the larger CoMP cells, and thus the border sub-cells, indicated by shading, may experience interference from transmissions in the border sub-cells of neighboring CoMP cells. The interference among multiple CoMP cells along the shaded border areas shown in FIG. 1 is referred to as inter-CoMP-cell interference. This type of interference still remains a major source of performance impairment.

An ultimate solution is to connect all of the sub-cells in all of the CoMP cells to a single central unit. However, this is not feasible in practice, especially for a large system deployment. The present invention provides an alternative solution that approximates the optimal solution without having a global central unit.

Within each CoMP cell, the interference is determined by the path gains between the UEs and their surrounding sub-cells. The central control unit scheduler attempts to group and order UEs to be served simultaneously by their attached sub-cells in a way such that a certain Signal-to-Interference-Ratio (SIR) target is met.

It is assumed that each cell knows the path gain between the base station and the UEs attached to it. The cells then communicate this information to the central unit, which then forms a path gain matrix:

${G = \begin{bmatrix} g_{11} & g_{12} & \ldots & \ldots & g_{1N} \\ g_{21} & g_{22} & \ldots & \ldots & g_{2N} \\ \vdots & \vdots & \ddots & \; & \vdots \\ \vdots & \vdots & \; & \ddots & \vdots \\ g_{M\; 1} & g_{M\; 2} & \ldots & \ldots & g_{MN} \end{bmatrix}},$

where g_(mn) is the path gain between the m'th UE and the n'th base station. For each UE iε{1, . . . , M}, there is a corresponding strongest base station σ(i), where

${\sigma (i)} = {\underset{j \in {\{{1,\ldots \mspace{14mu},N}\}}}{argmax}\; {g_{ij}.}}$

For each base station jε{1, . . . , N}, there is a corresponding strongest UE μ(j), where

${\mu (j)} = {\underset{i \in {\{{1,\ldots \mspace{14mu},M}\}}}{{argmax}\;}{g_{ij}.}}$

With this gain matrix, the central unit then performs the scheduling. The schedule essentially instructs each base station whether to transmit or not, and if so, to which UE and whether to schedule an uplink UE.

The present invention extends this concept by gathering additional information related to the scheduled UEs that are outside the CoMP cell under consideration but close enough to cause interference in the border sub-cells. The CoMP cell controller subsequently processes the augmented information to reduce the interference. The information communicated among neighboring CoMP cells can be as simple as the schedule, which is a list of the UEs selected to transmit or receive in the next transmit/receive phase. The description below describes the contents of the additional information, the way it is acquired, and how the augmented information is processed.

From a signal processing perspective, a CoMP system can be formulated as a linear system:

$\begin{matrix} {{\begin{bmatrix} r_{1} \\ r_{2} \\ \vdots \\ \vdots \end{bmatrix} = {{\begin{bmatrix} h_{11} & h_{12} & \ldots & \ldots \\ h_{21} & h_{22} & \ldots & \ldots \\ \vdots & \vdots & \ddots & \; \\ \vdots & \vdots & \; & \ddots \end{bmatrix}\begin{bmatrix} s_{1} \\ s_{2} \\ \vdots \\ \vdots \end{bmatrix}} + \begin{bmatrix} z_{1} \\ z_{2} \\ \vdots \\ \vdots \end{bmatrix}}},} & (1) \end{matrix}$

or more concisely,

r=Hs+z  (2)

where r is the received vector, H is the instantaneous channel state information, s is the transmit signal, and z is the Additive White Gaussian Noise (AWGN).

In many applications, the transmit signal s may be, but is not limited to, a linear function of the users' data symbols d given by:

s=Wd,  (3)

where W is sometimes referred to as a pre-coding matrix.

Note that these values are also a function of the frequency. This dependency is omitted for simplicity. The extension of what is disclosed here to a frequency selective system is straightforward.

This simple linear equation formulation will be used for both uplink and downlink calculations. For the uplink, the received vector r is available at the central controller and can therefore be jointly processed to detect the transmit vector s. For the downlink, on the other hand, r is available at the UEs that are not communicating with each other. The linear formulation is then used by the central controller to determine the transmit vector s such that interference can be mitigated without any UE's coordination.

In either case, the extent to which the elements in this formulation are known to the central controller will determine how well the system performs. One extreme case is that all sub-cells are connected to one single central controller at which the entire H matrix is available. Since there is only one CoMP cell, there is no inter-CoMP cell interference to deal with. In practice, however, there are multiple interfering CoMP cells that can only observe a subset of the elements in equation (1). This subset of observation can also be expressed in a matrix representation:

r _(D) =H _(D) s _(D) +z _(D).  (4)

If, in addition to equation (4), the CoMP cell also has access to some information from the neighboring CoMP cells, an augmented linear equation can be formed:

$\begin{matrix} {{{r_{A} \equiv \begin{bmatrix} r_{D} \\ r_{I} \end{bmatrix}} = {{\begin{bmatrix} H_{D} & H_{DI} \\ H_{ID} & H_{II} \end{bmatrix}\begin{bmatrix} s_{D} \\ s_{I} \end{bmatrix}} + \begin{bmatrix} z_{D} \\ z_{I} \end{bmatrix}}},{\equiv {{H_{A}s_{A}} + z_{A}}}} & (5) \end{matrix}$

where r_(I) is a subset of the received vector in neighboring CoMP cells, Z_(I) is the corresponding AWGN, and (H_(DI), H_(ID), H_(II)) are the associated channel matrices. The present invention is concerned with such a basic architecture and may be implemented in an exemplary embodiment as follows.

Information to be Communicated

The information communicated among neighboring CoMP cells can be as simple as the schedule, which is a list of the UEs selected to transmit or receive in the next transmit/receive phase. The schedule essentially identifies the active elements in the channel matrices. It can also be any part of the linear equation including the channel matrices, the transmit vector, the pre-coding matrix, the receive vector, or the statistics of the AWGN.

On the uplink, for example, the interfering CoMP cells may inform the desired CoMP cell of the uplink UEs the interfering CoMP cells have scheduled. Thus, the desired CoMP cell has:

$\begin{matrix} {r_{D} = {{\begin{bmatrix} H_{D} & H_{DI} \end{bmatrix}\begin{bmatrix} s_{D} \\ s_{I} \end{bmatrix}} + z_{D}}} & (6) \end{matrix}$

to work with. The matrix H_(DI) is the uplink channel between the sub-cells in the desired CoMP cell and the scheduled UEs in the neighboring CoMP cells. The matrix H_(DI) can be estimated from the pilot signal transmitted by the UEs on the uplink.

On the downlink, the interfering CoMP cells may inform the desired CoMP cells the UEs they have scheduled along with their corresponding channel matrix H_(ID) so that it has

$\begin{matrix} {\begin{bmatrix} r_{D} \\ r_{I} \end{bmatrix} = {{\begin{bmatrix} H_{D} \\ H_{ID} \end{bmatrix}s_{D}} + \begin{bmatrix} z_{D} \\ z_{I} \end{bmatrix}}} & (7) \end{matrix}$

to work with. The desired CoMP cell can then design the transmit signal s_(D) to avoid causing interference to the scheduled UEs in the neighboring CoMP cells. Note that the matrix H_(ID) is the downlink channel between the scheduled UEs in the neighboring CoMP cells and the sub-cells in the desired CoMP cell. The matrix H_(ID) needs to be explicitly communicated in a Frequency Division Duplex (FDD) system. However, if the system is a Time Division Duplex (TDD) system, the matrix H_(ID) can be measured on the uplink based on the theory of reciprocity.

Finally, the desired CoMP cell may obtain all the channel matrices in equation (5)Error! Reference source not found. from methods to be described later and has access to the full augmented linear equation:

r _(A) =H _(A) s _(A) +z _(A).  (8)

The downlink transmission and uplink reception can then be designed accordingly as if it were a self-contained, single CoMP cell system.

Information Gathering

FIG. 3 is an illustrative drawing of a grouping of CoMP cells in a system deployment in an embodiment of the present invention. The schedules and channel matrices mentioned above may be exchanged among the involved CoMP cells through an existing backbone network or other suitable connections. In some cases, the UEs may also serve as relays by communicating channel information within the desired CoMP cell to neighboring non-serving CoMP cells. Alternatively, the bordering sub-cells may be connected to multiple neighboring CoMP cells as shown in FIG. 3.

Conventionally, each CoMP cell in FIG. 3 consists of the non-overlapping sub-cells marked by different patterns. In embodiments of the present invention, an architecture is utilized in which the sub-cells in the border areas are connected to more than one neighboring CoMP cell controllers. For example, sub-cells {s₀₂, s₁₂, s₂₂} are connected to CoMP cells {C₀, C₁, C₂}, and sub-cells {s₀₁, s₂₁} are connected to CoMP cells {C₀, C₂}. This essentially extends the observation beyond the original CoMP cell boundary into neighboring CoMP cells. Therefore, from the observation point of view, the extended CoMP cells have borders marked by the overlapping thick lines. However, even though an extended CoMP cell has access to the sub-cells in neighboring CoMP cells, it still only processes the transmissions and receptions of the UEs within its original border.

There are occasions when the scheduling and transmission decisions of a CoMP cell depend on the decisions made by the neighboring CoMP cells. For example, a CoMP cell may be able to determine the optimal set of UEs to schedule if the UEs scheduled in neighboring CoMP cells are known. In another example, a CoMP cell may be able to best design its pre-coding matrix if the pre-coding matrix of neighboring CoMP cells are known. In these cases, the present invention may establish among the CoMP cells, a hierarchical relationship in which scheduling information from a first set of CoMP cells is passed to neighboring CoMP cells to assist in their scheduling.

FIGS. 4A and 4B are illustrative drawings of a scheduling hierarchy among a grouping of CoMP cells in an exemplary embodiment of the present invention. In order to mitigate the inter-CoMP-cell interference among border sub-cells in neighboring CoMP cells, the multiple CoMP cells in a system deployment are grouped into a number of mutually exclusive subsets such as A, B, and C. The CoMP cells in each subset are sufficiently separated from each other that no inter-cell interference occurs among them and therefore they can be scheduled independently. Each subset then takes turn scheduling transmissions in its sub-cells in a certain order (for example, subset A, followed by subset B, and then subset C as shown in the illustrated example). As each subset schedules its transmissions, it avoids causing interference to subsets that have already scheduled, and then passes sufficient information to the remaining subsets so that the same interference avoidance measures can be taken. The scheduling and information passing preferably all transpire before the data transmission phase, which occurs once every TTI.

Referring to FIG. 4A, the CoMP cells in subset A send information regarding the scheduling of their border sub-cells to all six of their neighboring CoMP cells so that the neighboring CoMP cells can take adequate action to avoid generating interference to the A cells. Once this process is completed, the B cells broadcast such information to the C cells as shown in FIG. 4B. Because of the action that the B cells have taken, little or no interference is generated to the A cells. The B cells only need to broadcast the appropriate information to the C cells so that the C cells can take the necessary action to avoid generating interference to both the A cells and B cells. The C cells do not need to broadcast any information since they are the last to perform the scheduling action.

Referring again to FIG. 3, assume that the scheduling hierarchy is left cross-hatched cells (C1,C3,C5) first, right cross-hatched cells (C2,C4,C6) second, and then the vertically cross-hatched cell (C0) third. CoMP-controller C1 may schedule the sub-cells of its CoMP cell first. In particular, the weights of sub-cell S12 are optimized in order to mitigate intra-COMP-cell interference. Second, the CoMP-controller C2 schedules. Because CoMP-controller C2 is connected to S12, C2 knows the weights of S12 and schedules neighbor sub-cell S22 and all other sub-cell S2 x so that inter-COMP-cell interference is mitigated. Of course the performance of the COMP-cell is maximized and intra-COMP-cell interference is considered in the scheduling decision as well. Finally, the weights of S22 are set. Third, CoMP controller C0 schedules. COMP-controller C0 knows the weights of S12 and S22. So the weights for S02 and all other sub-cell S0 x are optimized taking the schedules/weights of S22 and S12 into account. Finally the sub-cells S02, S22 and S12 are cooperatively scheduled.

In the given example, the border sub-cell, e.g., a radio head, will have a buffer that stores the commands (weights) from the CoMP controllers so that they can be shared afterwards. The weights and the associated schedule of bordering sub-cells may be passed in the hierarchical order, for example, through a switched/routed backbone network or through a dedicated point-to-point or point-to-multipoint connection between a border sub-cell and its neighboring CoMP cell controller.

Information Processing—Uplink

On the uplink, the pre-coding matrix is usually an identity matrix since there is no coordination among the UEs to reshape the transmit signal. The information processing then lies on the receiver design based on the augmented observation. One simple example is the MMSE receiver given by:

ŝ _(D) =E{s _(D) s _(A) ^(H) }H _(A) ^(H)(H _(A) E{s _(A) s _(A) ^(H) }H _(A) ^(H) +E{z _(A) z _(A) ^(H)})⁻¹ r _(A)  (9)

where E{.} and ( )^(H) denote the expected value and Hermitian transpose respectively.

Information Processing—Downlink

On the downlink, the information processing depends on the pre-coding matrix design. In one embodiment, each CoMP cell designs the pre-coding matrix based on the augmented observation using methods such as zero-forcing. For those sub-cells that are connected to more than one CoMP cell, their transmission weights are then set to the sum of the weights from the CoMP cells to which they are connected.

FIG. 5 is a flow chart illustrating the steps of an exemplary embodiment of the method of the present invention. The illustrated embodiment is based on a scenario involving three CoMP cells, each of which includes a plurality of contiguous sub-cells and a CoMP cell controller operative to manage transmissions within the sub-cells of each respective CoMP cell to minimize intra-CoMP cell interference. At step 21, a hierarchical scheduling order is defined in which the first CoMP cell controller schedules transmissions in the sub-cells of the first CoMP cell, and then the second CoMP cell controller schedules transmissions in the sub-cells of the second CoMP cell, and then the third CoMP cell controller schedules transmissions in the sub-cells of the third CoMP cell. At step 22, the first CoMP cell controller schedules transmissions in the sub-cells of the first CoMP cell. At step 23, after the transmissions in the sub-cells of the first CoMP cell are scheduled, the second CoMP cell controller gathers scheduling information for sub-cells in the first CoMP cell that border the second CoMP cell. At step 24, the intra-CoMP cell scheduling information in the second CoMP cell is augmented with the scheduling information from the bordering sub-cells in the first CoMP cell to create augmented scheduling information for the second CoMP cell. At step 25, the second CoMP cell controller utilizes the augmented scheduling information for the second CoMP cell to schedule transmissions to and from UEs within the sub-cells of the second CoMP cell to reduce the inter-CoMP cell interference with the first CoMP cell.

At step 26, after the transmissions in the sub-cells of the second CoMP cell are scheduled, the third CoMP cell controller gathers scheduling information for sub-cells in the first and second CoMP cells that border the third CoMP cell. At step 27, the intra-CoMP cell scheduling information in the third CoMP cell is augmented with the scheduling information from the bordering sub-cells in the first and second CoMP cells to create augmented scheduling information for the third CoMP cell. At step 28, the third CoMP cell controller utilizes the augmented scheduling information for the third CoMP cell to schedule transmissions to and from UEs within the sub-cells of the third CoMP cell to reduce the inter-CoMP cell interference with the first and second CoMP cells.

It should be noted that the augmented scheduling information may also include one or more of a transmit vector, a receive vector, a pre-coding matrix, channel matrices, or statistics of the AWGN. This enables the second and third CoMP cell controllers to output transmit waveform information for further minimizing interference in addition to scheduling the transmissions.

FIG. 6 is a simplified block diagram of an exemplary embodiment of the CoMP cell controller 11 according to the teachings of the present invention. The CoMP cell controller is communicatively linked to the plurality of base stations in the sub-cells of the associated CoMP cell. A scheduling processor 31 schedules transmissions to and from UEs in the sub-cells of the CoMP cell to minimize intra-CoMP-cell interference among the sub-cells within the CoMP cell. As noted above, the processor may also output transmit waveform information.

The scheduling processor 31 runs computer program instructions stored on a memory 32. When the instructions are run, the scheduling processor schedules transmissions such that no UE in the CoMP cell experiences interference greater than a defined threshold. Alternatively, the processor may schedule transmissions such that the total interference experienced by a given UE does not exceed a defined threshold. In other words, the scheduling processor schedules transmissions such that the total interference experienced by any of the UEs does not result in a signal-to-interference ratio (SIR) budget being exceeded.

As previously noted, the CoMP cells in the network are divided into mutually exclusive subsets, and the CoMP cells in the different subsets may rotate the order in which they schedule their transmissions. Thus, any given CoMP cell controller 11 may be in the first, second, or third subset to schedule, given the scenario described above. If the CoMP cell is in the first or second subset to schedule, a first interface (Interface-1) 33 is used to send scheduling information from the CoMP cell controller to neighboring CoMP cells that have not yet scheduled. If the CoMP cell is the second or third subset to schedule, a second interface (Interface-2) 34 is used to receive scheduling information in the CoMP cell controller from neighboring CoMP cells that have finished scheduling. The scheduling processor 31 may also accept path gains, a channel matrix, and pre-coding matrix as inputs. The processor then generates the scheduling information and transmit waveform information for transmissions in its associated CoMP cell.

The present invention, as described in embodiments above, improves CoMP performance by extending the observation set over relevant bordering sub-cells. The improvement is most significant for UEs experiencing greater inter-CoMP cell interference along the border. One-to-many associations between a sub-cell and neighboring CoMP cells enables fast information sharing.

FIG. 7 is a graphical representation of simulation results for the uplink processing utilizing Equation (9) above. The CoMP cell in the simulation consists of 21 sub-cells. One additional ring of sub-cells are included as augmented observations similar to FIG. 3. The baseline prior art processes only the observation made by the 21 sub-cells. The improvement in user data rate is approximately 0.75 bit/sec/Hz.

As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed above, but is instead defined by the following claims. 

1. A method of reducing interference in a wireless communication network comprising a first Coordinated Multi-Point (CoMP) cell and a neighboring second CoMP cell, wherein each CoMP cell comprises a plurality of contiguous sub-cells and a CoMP cell controller operative to manage transmissions within the sub-cells of the CoMP cell to minimize intra-CoMP cell interference, the method comprising the steps of: gathering by the first CoMP cell controller, scheduling information for an external sub-cell in the neighboring second CoMP cell, said external sub-cell being located such that transmissions to and from user equipments (UEs) within the external sub-cell cause inter-CoMP cell interference in a given sub-cell in the first CoMP cell; augmenting intra-CoMP cell scheduling information in the first CoMP cell with the scheduling information for the external sub-cell to create augmented scheduling information; and utilizing the augmented scheduling information to schedule, by the first CoMP cell controller, transmissions to and from UEs within the given sub-cell in the first CoMP cell to reduce the inter-CoMP cell interference.
 2. The method according to claim 1, wherein the external sub-cell in the neighboring second CoMP cell is a border sub-cell adjacent to the given sub-cell in the first CoMP cell.
 3. The method according to claim 1, wherein the gathering step includes gathering the scheduling information through one of: a switched backbone network that connects the first CoMP cell controller with the second CoMP cell controller; and a dedicated point-to-point connection between the first CoMP cell controller and the second CoMP cell controller.
 4. The method according to claim 1, wherein the gathering step includes gathering a list of the UEs selected to transmit or receive in the external sub-cell in a next transmit/receive phase.
 5. The method according to claim 4, wherein the augmented scheduling information also includes one or more of a transmit vector, a receive vector, a pre-coding matrix, channel matrices, or statistics of the Additive White Gaussian Noise (AWGN).
 6. A method of reducing interference in a wireless communication network comprising a first Coordinated Multi-Point (CoMP) cell and a neighboring second CoMP cell, wherein each CoMP cell comprises a plurality of contiguous sub-cells and a CoMP cell controller operative to manage transmissions within the sub-cells of the CoMP cell to minimize intra-CoMP cell interference, the method comprising the steps of: gathering by the first CoMP cell controller, scheduling information from a plurality of external sub-cells in the neighboring second CoMP cell, said external sub-cells being located such that transmissions to and from user equipments (UEs) within the external sub-cells cause inter-CoMP cell interference in at least one sub-cell in the first CoMP cell; augmenting intra-CoMP cell scheduling information in the first CoMP cell with the scheduling information from the plurality of external sub-cells to create augmented scheduling information; and utilizing the augmented scheduling information to schedule, by the first CoMP cell controller, transmissions to and from UEs within the at least one sub-cell in the first CoMP cell to reduce the inter-CoMP cell interference.
 7. The method according to claim 6, wherein the plurality of external sub-cells in the neighboring second CoMP cell are border sub-cells adjacent to the at least one sub-cell in the first CoMP cell.
 8. The method according to claim 6, wherein the gathering step includes gathering the scheduling information through one of: a switched backbone network that connects the first CoMP cell controller with the second CoMP cell controller; and a dedicated point-to-point connection between the first CoMP cell controller and the second CoMP cell controller.
 9. The method according to claim 6, wherein the gathering step includes gathering a list of the UEs selected to transmit or receive in each of the external sub-cells in a next transmit/receive phase.
 10. The method according to claim 9, wherein the augmented scheduling information also includes one or more of a transmit vector, a receive vector, a pre-coding matrix, channel matrices, or statistics of the Additive White Gaussian Noise (AWGN).
 11. A method of reducing interference in a wireless communication network comprising a first Coordinated Multi-Point (CoMP) cell having a plurality of contiguous sub-cells and a first CoMP cell controller operative to manage transmissions within the sub-cells of the first CoMP cell to minimize intra-CoMP cell interference, a neighboring second CoMP cell having a plurality of contiguous sub-cells and a second CoMP cell controller operative to manage transmissions within the sub-cells of the second CoMP cell to minimize intra-CoMP cell interference, and a neighboring third CoMP cell that neighbors both the first and second CoMP cells and includes a plurality of contiguous sub-cells and a third CoMP cell controller operative to manage transmissions within the sub-cells of the third CoMP cell to minimize intra-CoMP cell interference, the method comprising the steps of: defining a hierarchical scheduling order in which the first CoMP cell controller schedules transmissions in the sub-cells of the first CoMP cell, and then the second CoMP cell controller schedules transmissions in the sub-cells of the second CoMP cell, and then the third CoMP cell controller schedules transmissions in the sub-cells of the third CoMP cell; after the transmissions in the sub-cells of the first CoMP cell are scheduled, gathering by the second CoMP cell controller, scheduling information for sub-cells in the first CoMP cell that border the second CoMP cell; augmenting intra-CoMP cell scheduling information in the second CoMP cell with the scheduling information from the bordering sub-cells in the first CoMP cell to create augmented scheduling information for the second CoMP cell; and utilizing the augmented scheduling information for the second CoMP cell to schedule, by the second CoMP cell controller, transmissions to and from UEs within the sub-cells of the second CoMP cell to reduce the inter-CoMP cell interference with the first CoMP cell; after the transmissions in the sub-cells of the second CoMP cell are scheduled, gathering by the third CoMP cell controller, scheduling information for sub-cells in the first and second CoMP cells that border the third CoMP cell; augmenting intra-CoMP cell scheduling information in the third CoMP cell with the scheduling information from the bordering sub-cells in the first and second CoMP cells to create augmented scheduling information for the third CoMP cell; and utilizing the augmented scheduling information for the third CoMP cell to schedule, by the third CoMP cell controller, transmissions to and from UEs within the sub-cells of the third CoMP cell to reduce the inter-CoMP cell interference with the first and second CoMP cells.
 12. A Coordinated Multi-Point (CoMP) cell controller in a first CoMP cell for reducing interference in a wireless communication network in which the first CoMP cell neighbors a second CoMP cell, wherein each CoMP cell comprises a plurality of contiguous sub-cells, the CoMP cell controller comprising: means for gathering scheduling information for an external sub-cell in the neighboring second CoMP cell, said external sub-cell being located such that transmissions to and from user equipments (UEs) within the external sub-cell cause inter-CoMP cell interference in a given sub-cell in the first CoMP cell; means for augmenting intra-CoMP cell scheduling information in the first CoMP cell with the scheduling information for the external sub-cell to create augmented scheduling information; and means for utilizing the augmented scheduling information to schedule transmissions to and from UEs within the given sub-cell in the first CoMP cell to reduce the inter-CoMP cell interference.
 13. The CoMP cell controller according to claim 12, wherein the external sub-cell in the neighboring second CoMP cell is a border sub-cell adjacent to the given sub-cell in the first CoMP cell.
 14. The CoMP cell controller according to claim 12, wherein the means for gathering includes an interface to one of: a switched backbone network that connects the first CoMP cell controller with the second CoMP cell controller; and a dedicated point-to-point connection between the first CoMP cell controller and the second CoMP cell controller.
 15. The CoMP cell controller according to claim 12, wherein the scheduling information includes a list of the UEs selected to transmit or receive in the external sub-cell in a next transmit/receive phase.
 16. The CoMP cell controller according to claim 15, wherein the augmented scheduling information also includes one or more of a transmit vector, a receive vector, a pre-coding matrix, channel matrices, or statistics of the Additive White Gaussian Noise (AWGN).
 17. A Coordinated Multi-Point (CoMP) cell controller in a first CoMP cell for reducing interference in a wireless communication network in which the first CoMP cell neighbors a second CoMP cell, wherein each CoMP cell comprises a plurality of contiguous sub-cells, the CoMP cell controller comprising: means for gathering scheduling information from a plurality of external sub-cells in the neighboring second CoMP cell, said external sub-cells being located such that transmissions to and from user equipments (UEs) within the external sub-cells cause inter-CoMP cell interference in at least one sub-cell in the first CoMP cell; means for augmenting intra-CoMP cell scheduling information in the first CoMP cell with the scheduling information from the plurality of external sub-cells to create augmented scheduling information; and means for utilizing the augmented scheduling information to schedule transmissions to and from UEs within the at least one sub-cell in the first CoMP cell to reduce the inter-CoMP cell interference.
 18. The CoMP cell controller according to claim 17, wherein the plurality of external sub-cells in the neighboring second CoMP cell are border sub-cells adjacent to the at least one sub-cell in the first CoMP cell.
 19. The CoMP cell controller according to claim 17, wherein the means for gathering includes an interface to one of: a switched backbone network that connects the first CoMP cell controller with the second CoMP cell controller; and a dedicated point-to-point connection between the first CoMP cell controller and the second CoMP cell controller.
 20. The CoMP cell controller according to claim 17, wherein the scheduling information includes a list of the UEs selected to transmit or receive in each of the external sub-cells in a next transmit/receive phase.
 21. The CoMP cell controller according to claim 20, wherein the augmented scheduling information also includes one or more of a transmit vector, a receive vector, a pre-coding matrix, channel matrices, or statistics of the Additive White Gaussian Noise (AWGN). 